Radio signaling system



Feb. 12, 1929.. 1,701,591

w."r. POWELL RADIO SIGNALING SYSTEM Filed Sept. 12 1925 IN PUT p. i N vo 8 5 zo G Ill U D l 45 l I Fl G. 3 ANTENNA STAGE '1 smsa'z smcaa I OFOF or 1 2 LOUD ammo ammo ammo DEFECT Aumo AUDIO :PEAKLR FREQUENCYF'QEQUENCY EEQkLNC-Y INVENTOR \VIHFRED T. POWELL.

' ATTORNEY latentecl Feb. 12, 1929.

winrnnn r. POWELL, or nocnnsrnn, NnwfYonK, Assienoa TO THE STROMBERG--'1,701,591 PATENT, oFF ca.

GABLSON TELEPHONE MANUFACTURING COMPANY, OF ROCHESTER, NEW YORK,

A CORPORATION NEW YORK.

RADIO SIGNALING I SYSTEM.

Application filed September 12, 1925. Serial No. 55,968.

This invention relates to signaling systems and more particularly toamplifying arrangements for use in such systems. V

In multi-stage, radio-frequency amplifying systems using a thermionictube and associated circuits in each stage, great difficulty has beenexperienced in eliminating undesirable oscillations, resulting inaudible noises, which disturb or drown out the signal to be received;These oscillations, for the most part, are due to the phenomenon knownasfeed-back, wherein energy from the output circuit of a thermionic tubeis returned to the input circuit thereof, throughthe inherent gridrplatecapacity of the. tube, causing at certain frequencies increasedexaggerated amplification, limited only by the constants of the circuitsand the characteristics of the tube. i

The object of the present invention is to provide an improved method ofeliminating the effect of capacity coupling between the input and outputcircuits of each stageof a radio-frequency amplifier:

The novel features characteristic of the present invention will appearfrom the detailed description and appended claims.

For an understanding of the invention, ref erence is made to thedrawings, in which Fig. 1 is a diagrammatic circuit arrangement in theform of an impedance bridge representing one stage of a multi-stageradio-frequency amplifier. I

Fig. 2 is a portion of an amplifying system in which the part within thedotted rectangle shows the circuits which are diagrammaticallyrepresented inFig. 1. Atthe left of the rectangle there is indicated theoutput circuit of a vacum tube in a preceding stage, or it maybe anantenna or other signal intercepter. At the right of the rectangle thereis indicated the tuned portion of an input circuit of a detector (notshown).

Fig. 3 is a diagrammatic showing of a multi-stage radio. receivingsystem, having three stages of radio-frequency amplification, a detectorand two stages of audio amplification.

Referring especially to Fig. 2, 5 designates theprimary winding of atransformer included in the output circuit ofa thermionicradio-frequency amplifier. The secondary winding 6 of this transformerhas connected across its terminals a variable condenser 7,

which with the inductance of thewinding 7 serves to variably tune theinput circuit of the thermionic tube, generally designated 8. The grid 9of this tube is connected to a point on the circuit connecting theterminals of the secondary winding 6 and the condenser 7, while theplate 10 of the thermionic tube 8 is connected through a compensatingfixed condenser llto a point on the circuit connecting the other twoterminals of the condenser 7 and the secondary winding 6. As is wellknown the filament 12 has a heating circuit including a source ofheating current 13, controlled by arheostat 14. The output circuit ofthe thermionic tube 10 extends from the plate 10 through the primarywinding 15 of a second transformer, plate battery-16, and conductor 17to one side of the filament heating system. A coil 18 wound in the samecircuit of a detector, which is tuned by the variable condenser'QO. Thisdetector may be of any well known type, preferably a I thermionicdetector.

The circuits just described form an im pedance bridge arrangement, inwhich the input circult 18 coupled across two sets of arms of thebridge, while the output circuit is 1 coupled across a set of two otherarms of the bridge. Although the output circuit is not conductivelyconnected to point 22 on coil 6,

the coil 18 inductively connects the output circuit to this point, sothat by varying the coupling of coil 18 with respect to the winding 6,the position of point 22 may be varied. By this bridge arrangementelectrical energy in the output circuit of a thermionic tube has noeffect on the input circuit thereof. As shown in Fig. 1, one of the armsof the bridge includes the inherent capacity 21 existing between thegrid 9 and the plate 10 of the thermionic tube. Another arm of thebridge includes the capacity of the fixed cong from the point designated22 to each terminal of the winding. In determining the constants of thecircuit of Fig. 2, the various elements are so selected that the productof the rcactance of the condenser 11 and the reactance of the upperportion of the coil 6 is equal to the reactance of the lower portion ofthe coil 6, and the reactance effector the inherent grid-plate electrodecapacity 21. Under these conditions of balance in the bridge, anyelectrical condition existing between the plate 10 and the point on thecoil 18, associated with the point 22 will have no effect on the inputcircuit, since the point 23 and the point on the bridge connected to thegrid 9 are of the same potential as far as the currents in the outputcircuit are concerned. However, when an incoming signal current ispresent in the inputcircuit of the bridge, a difference of potential isset up betv-Jeen the filament l2 and the grid 8, which results incausing the thermionic tube 8 to amplify the signal in the well knownmanner.

The schematic showing of Fig. 3 indicates a tuned radio-frequencyamplifying radio receiving system, in which each of the radio-frequencyamplifying stages agtl to #3 inclusive, may be of the arrangen'ientshown within the dotted rectangle of Fig. 2.-

The detector 24 may be of any well known form and has associatedtherewitl audiotrequency amplifiers 25 and 26 by which the rectifiedsignal is amplified for reproduction in a loud speaker or otherindicating device.

lVhat I claim is: V

1. In an amplifier, an electron discharge device having grid, filamentand plate electrodes, a tuned input circuit having included therein asecondary winding of a coupling transformer and a variable condenser,said input circuit being connected at one end to said grid and beingconnected at its other end to said filament through a coil closelycoupled to said secondary winding, a com- 'pensating condenser connectedto said plate and to a point on the conductor extending between saidcoil and said winding, and an output circuit. connected to said plateand said filament.

2. In a signaling system, an electron dis charge device provided withfilament, grid and plate electrodes having inherent capacity existingtherebetween, an input circuit and -an output circuit for said device, atransformer having a secondary winding included in said input circuit,said electron discharge device and secondary winding being con nected inan impedance bridge, the inherent capacity between said grid and platebeing included in one of the arms of said bridge a compensating capacityconnected in another arm of said bridge, portions of said secondarywinding being connected as the other two arms of said bridge, terminalsof said input circuit being connected to conugate points on said bridge,an output (311'- cuit'conductively connected at one of its ends andinductively connected at its other end to another pair of conjugatepoints on said the grid and the plate electrodes forming one arm of saidbridge, a compensating condenser connected between said plate electrodeand a common point on said bridge forming a.

second arm of saidbridge a secondary wind- I ing of a transformer beingconnected between the grid and said common point to form the other twoarms of'said bridge, an input circuit for said discharge tube includingsaid secondary winding connecting said grid and filament, an outputcircuit. connecting said plate and filament, and a coil in series with aconductor extending from said common point to said filament, said coilbeing inductively connected to an intermediate point on said secondarywinding.

In witness whereof, I hereunto subscribe my name this 10th day ofSeptember A. D. 1925.

VVI'NFRED 'l. POVV'ELL.

